Model Orchestration

Model Orchestration Policy

A fixed role split between model tiers, set by the user (2026-07-04, revised 2026-07-07). The premise is quality-over-cost: delegation floors are set at the effort levels Anthropic itself recommends for intelligence-sensitive work ("start with xhigh for coding and agentic use cases, high as the minimum for most intelligence-sensitive workloads" — official effort guidance), not at the cost-saving end ("low ... like subagents"). When this policy and a cost instinct conflict, the policy wins; surface the cost, don't silently downgrade.

Role split

| Role | Who | Effort floor | Duties | |------|-----|--------------|--------| | Orchestrator + Product Manager | Top-tier session model (Fable) | session level | Directs everything. Directly: 서비스 방향성 수립·논의, 기획/스펙문서 리뷰, 기개발 기능 개선, 문제점(성능·보안) 발굴 — see below | | Doc author + core builder + V&V | opus | xhigh (or max) | 기획/스펙/계획 문서 작성·관리, 핵심 구현(novel logic · architecture-touching · security surface), V&V | | Repetitive implementation + E2E | sonnet | high (or above) | 반복 구현(pattern-following, boilerplate, example-driven migrations), E2E 테스트 작성·실행, research sweeps | | Orchestrator stand-in (quota exhausted) | opus @ max | max | Takes over orchestration via a handoff — see "Orchestrator handoff" |

The orchestrator assigns a thinking/effort level per task at delegation time. Delegating below a floor is a policy violation, not a tuning choice.

The orchestrator's own lane: direction, review, judgment

The orchestrator authors direction, not documents. 서비스 방향성(where the product goes), 스펙 리뷰(is this plan right?), 기능 개선(what should get better in what shipped?), and 성능·보안 문제 발굴 stay in the orchestrator's window — that's where user intent, constraints, and history live, and judgment is the one thing a delegation prompt can't carry.

Document drafting is delegated to Opus with a direction brief (intent, constraints, decided trade-offs). This buys an author≠reviewer split for documents themselves: Opus writes, the orchestrator reviews — a draft you review with fresh eyes gets scrutiny your own draft never would. For 기획/스펙문서 리뷰, run the [[multi-persona-review]] skill (3–5 disjoint persona reviewers, severity-ranked synthesis) instead of a single-pass read; the orchestrator arbitrates its findings rather than line-editing alone.

Routing test: repetitive vs core

Before routing to any model: deterministic transforms don't get a model at all. A rename, a format sweep, a mechanical find-and-replace is sed/grep/script work — spending model tokens on what code answers deterministically fails the routing test at step zero.

Route to Sonnet (반복 구현 · E2E) when ALL of these hold; otherwise it's Opus core work:

• The task is repetitive or example-driven — a pattern already exists to follow (an

adjacent implementation, a spec with worked examples, a test suite to extend). Acceptance criteria fit in a few lines without "use judgment" clauses.

• It's low-blast-radius: boilerplate, N-th instance of an established shape, E2E test

authoring/execution, a research sweep. A wrong answer is cheap to detect and redo.

• It needs no architectural or cross-cutting decisions. Actions carry implicit decisions;

a worker making design choices in isolation silently diverges from the system (the classic parallel-agent failure).

Core implementation — novel logic, first-of-its-kind shapes, ambiguity, security surface, multi-file coupling — routes to Opus @ xhigh+, as does all verification duty. When unsure, route up — the cost delta is smaller than a redo.

Parallelism rule of thumb (three independent sources converge on this): parallel reads are safe, parallel writes are dangerous. Fan out freely for research/search/review; keep writes sequential or isolated (worktree) so two workers never make conflicting implicit decisions in the same files.

Effort floors — and the inheritance gotcha

Effort tiers: low .md` frontmatter pins both knobs. This is the durable path for recurring roles:

``yaml --- name: verifier description: Fresh-context V&V per model-orchestration policy model: opus effort: xhigh --- ``

1. Workflow scripts — agent(prompt, {model: "opus", effort: "xhigh"}) supports both

per call. Use for scripted fan-outs.

1. Session inheritance — if the session already runs at xhigh (e.g. /effort xhigh or

ultracode), a bare Agent(model: "opus") inherits a compliant level. Verify with /effort; don't assume.

One environment caveat: CLAUDE_CODE_SUBAGENT_MODEL outranks every per-invocation and frontmatter model choice. If delegation models look wrong, check that env var first.

Delegation prompt spec

Every delegation carries these four elements (the exact set Anthropic found necessary after their orchestrator over-spawned and workers duplicated work), plus acceptance criteria:

1. Objective — one sentence, plus why it matters (models perform better knowing intent).
2. Output format — what comes back, in what structure. State that the final message IS the

deliverable (raw data, no user-facing preamble).

1. Tool/source guidance — where to look, what to trust, what to skip.
2. Boundaries — what NOT to touch, where the task ends, what is out of scope.
3. Acceptance criteria — how the worker (and you) know it's done. Strong AC lets the

worker loop independently instead of returning half-done.

Scale worker count to the task, stated up front in your own plan: trivial lookup → no agent at all (do it directly); bounded question → one agent; genuinely independent axes → one agent per axis. Over-spawning is a documented failure mode, and multi-agent runs cost ~15× a plain chat turn — delegate when the task's value justifies it, not by reflex.

V&V separation

The implementer never verifies its own work — the instance that wrote something never judges it. How that plays out per lane:

• Sonnet implemented (반복 구현/E2E) → Opus @ xhigh verifies (cross-model + fresh

context — catches classes of bugs same-model review does not).

• Opus implemented (핵심 구현) → a fresh Opus instance verifies: a NEW agent with no

shared history. A verifier that watched the implementation happen inherits the implementer's mental model and anchors on it — same-session self-review reliably misses the same edge cases the implementation missed. Instance separation is what makes "Opus builds AND Opus verifies" coherent.

• Orchestrator layer on top: the orchestrator hunts 성능·보안 문제점 in shipped features —

a second, higher-altitude pass that judges what a diff-level verifier doesn't (product fit, systemic risk). Documents get the same split: Opus authors, the orchestrator reviews via [[multi-persona-review]].

This pairs with, not replaces, deterministic gates (tests, typecheck, CI) — the verifier judges what automation can't: spec fit, missed edge cases, design drift.

Orchestrator handoff (quota exhaustion)

When the top-tier orchestrator's quota runs out mid-project, Opus @ max takes over orchestration. There is no reliable automatic path — documented fallback chains explicitly exclude rate-limit errors, and plan-level auto-switching is undocumented behavior you must not build on. Hand off manually:

1. Run the [[compaction-handoff]] protocol: persist durable facts to memory, take an atomic

git snapshot (clean tree + open-PR check), emit the fixed-field resume anchor (current state / verified / what's left / next action).

1. The successor session starts on opus at max (/model opus + /effort max), reads the

anchor, and continues as orchestrator under this same policy — setting direction, reviewing, and hunting problems itself (it can author documents directly too, since it already runs at the Opus doc-author tier — no separate delegation needed while it stands in).

1. When the top-tier model becomes available again, hand back the same way.

Anti-patterns

| Anti-pattern | Why it's a violation | |---|---| | Agent(model: "opus") with session at default effort | Inherits high < xhigh floor — use a pinned agent role, Workflow opts, or raise session effort | | Delegating 방향성 수립 or a final judgment call to a worker | Direction is the orchestrator's own — a delegation prompt can't carry the shaping context | | Accepting an Opus-authored spec/plan without orchestrator review | Author≠reviewer applies to documents too — run [[multi-persona-review]] before accepting | | Orchestrator hand-writing full spec/plan drafts itself | Authoring is Opus's lane — brief the direction, delegate the draft, review the result | | Sonnet on core work (novel / architectural / security) | Fails the routing test; route up to Opus | | Effort below floor "to save tokens" | The floors ARE the policy; surface cost concerns to the user instead | | Implementer verifying its own diff | Anchoring — verification needs fresh context, prefer a different model | | Two agents writing the same files in parallel | Conflicting implicit decisions; keep writes sequential or worktree-isolated | | Spawning an agent for what one direct tool call answers | 15× token multiplier for zero value — do trivial work directly | | Relying on plan-level auto-fallback for continuity | Undocumented behavior; use the manual handoff protocol |

Quick reference

방향성 수립 / 스펙 리뷰(multi-persona-review) / 기능 개선 / 성능·보안 문제발굴
                               → 오케스트레이터(Fable) 직접
기획·스펙·계획 문서 작성·관리 / 핵심 구현 / V&V
                               → opus  @ xhigh (또는 max)   — pinned role 또는 Workflow opts
반복 구현 / E2E 테스트 / 리서치 스윕
                               → sonnet @ high 이상
결정적 변환 (rename·포맷)      → 모델 위임 금지 — sed/grep/스크립트 직접
Fable 소진                     → compaction-handoff → opus @ max 가 오케스트레이터 대행

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: uzysjung
• Source: uzysjung/uzys-agent-harness
• License: MIT
• Homepage: https://uzysjung.github.io/uzys-agent-harness/

Install and usage instructions live in the source repository linked above.